WellPoint Inc. beat third-quarter earnings expectations and boosted its full-year forecast on Wednesday but remained cautious about next year, saying it is still too early to gauge the impact of the new health law.

While the Indianapolis-based insurer raised its 2013 earnings forecast, to $8.40 a share, Chief Financial Officer Wayne DeVeydt cautioned against expecting that "this improvement [will continue] into 2014, given the number of changes to our business" due to the federal health overhaul. However, Mr....